Images: The Ocean's Tiny Chemists

Marine microorganisms are the chemists of the ocean, continually cycling carbon and other chemicals via the routine biochemical reactions they use to live and grow. MIT/WHOI graduate student Kim Popendorf conducts a series of experiments to begin to tease apart the multitude of microbes in the ocean and determine which are performing which chemical reactions. The first step is to collect seawater containing microbes with an instrument known as a CTD. (Photo by Ruifeng Zhang, Woods Hole Oceanographic Institution)

Popendorf puts seawater into plexiglass containers on the deck of a ship and adds a heavy isotope of carbon, 13C. Different types of microorganisms take up different forms of carbon, which she can track via the heavy-carbon label. See interactive of entire process. (Photo by Kim Popendorf, MIT/WHOI Joint Program)

After allowing the microbes to incorporate the 13C into their cell membranes, Popendorf filters the seawater through wafers with tiny pores to collect microbial cells. (Photo by Michal Koblížek, Czech Academy of Sciences)

The greenish tinge on the filters are microbial cells. Each filter has more than a quarter of a billion cells on it. (Photo by Kim Popendorf, MIT/WHOI Joint Program)

Back in a lab on shore, the cells are injected into a liquid chromatography apparatus. It separates out individual types of lipids from the cell membranes in the cells that Popendorf collected. Using the 13C carbon label, she can begin to determine which types of microbes made which lipids. (Photo by Kim Popendorf, MIT/WHOI Joint Program)